The present invention relates generally to sandwich constructions suitable for use in structural and non-structural members, and more particularly to sandwich constructions of low-density cores bonded between thin-gauge, high-strength face sheds for use in a wide range of military, industrial and commercial components.
Sandwich constructions are finding broad application as structural and non-structural members in boats, aircraft, furniture, appliances, and other items requiring high strength, light-weight materials. They typically include face sheets bonded to either side of a low density core and can be made of such materials as metals, plastics or composite fiberglass laminates for rigidity and strength. Among the various core materials are rigid plastic foams, honeycombs, truss-core corrugations and an arrangement of adjacent, inclined rectangular-shaped facets connected by intermediate rows of adjoining parallelagram-shaped facets.
In aircraft design the need for weight efficiency and aerodynamically smooth surfaces under high stress levels has stimulated use of sandwich construction as a possible substitute for the conventional sheet-stringer construction. Notwithstanding the superior weight-efficiency of the sandwich constructions, their general acceptance for critical applications has lagged behind theoretical development primarily because of maintenance problems experienced in service. Honeycomb core sandwich constructions, for instance, are considered to be among the most weight-efficient but, due to their tendency to retain moisture which may become entrapped due to ineffective edge seals or unbonding of face sheets from the core. This may degrade the structural integrity and lead to extensive corrosion and premature failure of components. Experience has shown a significant frequency of repairs on replacements which are very time-consuming and expensive.